For example, a projection type display apparatus that projects images on a projection surface such as a screen has been known. Such a projection type display apparatus includes an autofocus mechanism for adjusting the focal length of a projection lens that projects the images.
FIG. 1 is a perspective view of an autofocus mechanism included in a projection type display apparatus related to the present invention. As shown in FIG. 1, autofocus mechanism 101 includes projection lens 103, a lens support mechanism (not shown) that supports projection lens 103 movably in an optical axis direction, and focus ring 104 that moves projection lens 103 by using the lens support mechanism.
Autofocus mechanism 101 also includes detection gear 106 that rotates with rotation of focus ring portion gear 105 formed in focus ring 104, rotation detection element 107 that detects the amount of rotation of detection gear 106, drive motor 108 that drives focus ring portion gear 105, and a control circuit (not shown) that controls driving drive motor 108 on the basis of the detection result of rotation detection element 107.
Rotation detection element 107 is placed near an outer peripheral portion of focus ring 104, and a rotating shaft portion (not shown) of detection gear 106 is mounted in a shaft hole (not shown) in rotation detection element 107. Detection gear 106 meshes with focus ring portion gear 105. Rotation detection element 107 detects the rotation of focus ring 104 that rotates with the movement of projection lens 103 by using detection gear 106.
Drive motor 108 has a rotating shaft (not shown) to which drive gear 110 is mounted. Drive gear 110 meshes with focus ring portion gear 105, and drive motor 108 is rotationally driven to rotate focus ring 104.
FIG. 2 shows a flowchart that represents a process for controlling the autofocus mechanism. As shown in FIG. 2, the projection type display apparatus includes distance sensor 125 that detects a focal length, and on the basis of distance information measured by distance sensor 125, central processing unit (CPU) 126 of the control circuit controls driving drive motor 108 so that the output of rotation detection element 107 reaches a predetermined value to rotate focus ring 104, thereby adjusting focus.